Microporous sheet product and methods for making and using the same

Abstract

Microporous sheet product and methods of making and using the same. In one embodiment, the microporous sheet product is made by a process that includes melt-extruding a sheet material using an extrusion mixture that includes (i) a cyclic olefin copolymer, (ii) an electrolyte swellable thermoplastic, and (iii) a compatibilizing agent that promotes mixing of the cyclic olefin copolymer and the electrolyte swellable thermoplastic, the compatibilizing agent having a boiling point in the range of 135-300° C. As an example, the cyclic olefin copolymer may be an ethylene-norbornene copolymer, the electrolyte swellable thermoplastic may be polyethylene oxide, and the compatibilizing agent may be mineral spirits. After extrusion, the sheet material may be cooled, and the compatibilizing agent may be removed, forming an ionically-conductive microporous sheet product. The microporous sheet product has high-temperature stability and gels when exposed to a liquid electrolyte, enabling high ionic conductivity when used as a battery separator.

What is claimed is: 
     
       1. A microporous sheet product made by a method comprising (a) forming a mixture of (i) at least one cyclic olefin copolymer, (ii) an electrolyte swellable thermoplastic polymer, wherein the electrolyte swellable thermoplastic polymer is at least one member selected from the group consisting of polyoxyethylene, polypropylene oxide, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and a fluorocarbon terpolymer, and (iii) a compatibilizing agent that promotes mixing of the at least one cyclic olefin copolymer and the electrolyte swellable thermoplastic polymer, wherein the compatibilizing agent is a liquid hydrocarbon, the compatibilizing agent having a boiling point in the range of 135-300° C.; (b) casting the mixture to form a sheet material; and (c) cooling the sheet material, wherein the at least one cyclic olefin copolymer forms a continuous phase of the microporous sheet product and the electrolyte swellable thermoplastic polymer forms a discontinuous phase of the microporous sheet product, and wherein the microporous sheet product is free of polyethylene and polypropylene. 
     
     
       2. The microporous sheet product as claimed in  claim 1  wherein the at least one cyclic olefin copolymer comprises an ethylene-norbornene cyclic olefin copolymer. 
     
     
       3. The microporous sheet product as claimed in  claim 1  wherein the at least one cyclic olefin copolymer has a glass transition temperature of about 70-180° C. 
     
     
       4. The microporous sheet product as claimed in  claim 3  wherein the at least one cyclic olefin copolymer has a glass transition temperature above 90° C. 
     
     
       5. The microporous sheet product as claimed in  claim 4  wherein the at least one cyclic olefin copolymer has a glass transition temperature above 110° C. 
     
     
       6. The microporous sheet product as claimed in  claim 5  wherein the at least one cyclic olefin copolymer has a glass transition temperature above 130° C. 
     
     
       7. The microporous sheet product as claimed in  claim 1  wherein the at least one cyclic olefin copolymer has a glass transition temperature of 180° C., a heat deflection temperature of 170° C., a melt temperature of 270-320° C., and a volumetric flow index of 1.5 ml/10 min, tested at 260° C. and 2.16 kg load. 
     
     
       8. The microporous sheet product as claimed in  claim 1  wherein the at least one cyclic olefin copolymer has a molecular weight below 100,000 Da. 
     
     
       9. The microporous sheet product as claimed in  claim 8  wherein the at least one cyclic olefin copolymer has a molecular weight below 60,000 Da. 
     
     
       10. The microporous sheet product as claimed in  claim 9  wherein the at least one cyclic olefin copolymer has a molecular weight below 30,000 Da. 
     
     
       11. The microporous sheet product as claimed in  claim 1  wherein the at least one cyclic olefin copolymer constitutes about 10-70% by volume of the mixture. 
     
     
       12. The microporous sheet product as claimed in  claim 1  wherein the electrolyte swellable thermoplastic polymer includes at least one electronegative atom that promotes swelling when exposed to a suitable electrolyte. 
     
     
       13. The microporous sheet product as claimed in  claim 1  wherein the electrolyte swellable thermoplastic polymer is at least one member selected from the group consisting of polyoxyethylene and polyvinylidene fluoride-hexafluoropropylene-tetrafluoroethylene. 
     
     
       14. The microporous sheet product as claimed in  claim 1  wherein the electrolyte swellable thermoplastic polymer has a molecular weight above 30,000 Da. 
     
     
       15. The microporous sheet product as claimed in  claim 14  wherein the electrolyte swellable thermoplastic polymer has a molecular weight above 60,000 Da. 
     
     
       16. The microporous sheet product as claimed in  claim 15  wherein the electrolyte swellable thermoplastic polymer has a molecular weight above 100,000 Da. 
     
     
       17. The microporous sheet product as claimed in  claim 1  wherein the electrolyte swellable thermoplastic polymer has a higher molecular weight and a higher melt viscosity than the at least one cyclic olefin copolymer. 
     
     
       18. The microporous sheet product as claimed in  claim 1  wherein the electrolyte swellable thermoplastic polymer constitutes about 5-70% by volume of the mixture. 
     
     
       19. The microporous sheet product as claimed in  claim 1  wherein the compatibilizing agent has a boiling point in the range of about 170-250° C. 
     
     
       20. The microporous sheet product as claimed in  claim 19  wherein the compatibilizing agent has a flash point characteristic within the range of about 30-170° C. 
     
     
       21. The microporous sheet product as claimed in  claim 1  wherein the compatibilizing agent is a mixture of liquid hydrocarbons whose individual components have boiling points than span over a breadth of at least 10° C. 
     
     
       22. The microporous sheet product as claimed in  claim 21  wherein the compatibilizing agent is a mixture of liquid hydrocarbons whose individual components have boiling points than span over a breadth of at least 15° C. 
     
     
       23. The microporous sheet product as claimed in  claim 22  wherein the compatibilizing agent is a mixture of liquid hydrocarbons whose individual components have boiling points than span over a breadth of at least 20° C. 
     
     
       24. The microporous sheet product as claimed in  claim 1  wherein the compatibilizing agent comprises mineral spirits. 
     
     
       25. The microporous sheet product as claimed in  claim 1  wherein the compatibilizing agent constitutes about 10-90% by volume of the mixture. 
     
     
       26. The microporous sheet product as claimed in  claim 1  wherein the at least one cyclic olefin polymer constitutes about 10-70% by volume of the mixture, wherein the electrolyte swellable thermoplastic polymer constitutes about 5-70% by volume of the mixture, and wherein the compatibilizing agent constitutes about 10-90% by volume of the mixture. 
     
     
       27. The microporous sheet product as claimed in  claim 1  wherein the mixture further comprises at least one of an inorganic filler and a cross-linked polyacrylate polymer. 
     
     
       28. The microporous sheet product as claimed in  claim 1  wherein the method further comprises removing the compatibilizing agent from the sheet material. 
     
     
       29. The microporous sheet product as claimed in  claim 28  wherein the step of removing the compatibilizing agent comprises stretching the sheet material. 
     
     
       30. The microporous sheet product as claimed in  claim 1  wherein the method further comprises stretching the sheet material. 
     
     
       31. The microporous sheet product as claimed in  claim 1  wherein the microporous sheet product has a resistivity below 10,000 ohm-cm as tested in LiPF 6  electrolyte and below 300 as tested in a 30% KOH solution. 
     
     
       32. The microporous sheet product as claimed in  claim 31  wherein the microporous sheet product has a resistivity below about 3000 ohm-cm as tested in LiPF 6  electrolyte. 
     
     
       33. The microporous sheet product as claimed in  claim 1  wherein the microporous sheet product has an average pore size below 5 microns. 
     
     
       34. The microporous sheet product as claimed in  claim 1  wherein the mixture is an extrusion mixture and wherein the casting step comprises extruding the extrusion mixture to form the sheet material. 
     
     
       35. The microporous sheet product as claimed in  claim 1  wherein the mixture is a homogeneous solution and wherein the casting step comprises coating the homogeneous solution on a substrate using a solvent cast technique. 
     
     
       36. The microporous sheet product as claimed in  claim 35  wherein the substrate is a polyolefin film and wherein at least a portion of the homogeneous solution at least partially penetrates the polyolefin film. 
     
     
       37. A multilayer sheet product, the multilayer sheet product comprising a plurality of stacked layers, wherein at least one of the stacked layers is the microporous sheet product of  claim 1 . 
     
     
       38. The microporous sheet product as claimed in  claim 1  wherein the mixture further comprises an inorganic filler. 
     
     
       39. The microporous sheet product as claimed in  claim 1  wherein the mixture further comprises polyisobutylene. 
     
     
       40. The microporous sheet product as claimed in  claim 1  wherein the fluorocarbon terpolymer comprises a combination of three members of the group consisting of polyvinylidene fluoride, hexafluoral propylene, tetrafluoral ethylene, and chloro-trifluoral ethylene. 
     
     
       41. A method of separating the electrodes of a battery, the method comprising positioning the microporous sheet product of  claim 1  between the electrodes. 
     
     
       42. A method of packaging a food item, the method comprising contacting the food item with the microporous sheet product of  claim 1 . 
     
     
       43. A microporous sheet product made by a method comprising (a) dissolving at least one cyclic olefin copolymer and an electrolyte swellable thermoplastic polymer in a compatibilizing agent to form a homogeneous solution, wherein the electrolyte swellable thermoplastic polymer is at least one member selected from the group consisting of polyoxyethylene, polypropylene oxide, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and a fluorocarbon terpolymer and wherein the compatibilizing agent is a liquid hydrocarbon; and (b) forming a sheet material with the homogeneous solution using a solvent cast technique, wherein the at least one cyclic olefin copolymer forms a continuous phase of the microporous sheet product and the electrolyte swellable thermoplastic polymer forms a discontinuous phase of the microporous sheet product, and wherein the microporous sheet product is free of polyethylene and polypropylene. 
     
     
       44. A microporous sheet product made by a method comprising (a) forming a mixture of (i) at least one cyclic olefin polymer, (ii) an electrolyte swellable thermoplastic polymer, wherein the electrolyte swellable thermoplastic polymer is at least one member selected from the group consisting of polyoxyethylene, polypropylene oxide, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and a fluorocarbon terpolymer, and (iii) a compatibilizing agent that promotes mixing of the at least one cyclic olefin polymer and the electrolyte swellable thermoplastic polymer, wherein the compatibilizing agent is a liquid hydrocarbon, the compatibilizing agent having a boiling point in the range of 135-300° C.; (b) casting the mixture to form a sheet material; and (c) cooling the sheet material, wherein the at least one cyclic olefin polymer forms a continuous phase of the microporous sheet product and the electrolyte swellable thermoplastic polymer forms a discontinuous phase of the microporous sheet product, and wherein the microporous sheet product is free of polyethylene and polypropylene. 
     
     
       45. A method of making a microporous sheet product, the method comprising the steps of:
 (a) melt-extruding an extrusion mixture to produce a sheet material, the extrusion mixture comprising (i) at least one cyclic olefin copolymer, (ii) an electrolyte swellable thermoplastic polymer, wherein the electrolyte swellable thermoplastic polymer is at least one member selected from the group consisting of polyoxyethylene, polypropylene oxide, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and a fluorocarbon terpolymer, and (iii) a compatibilizing agent that promotes mixing of the at least one cyclic olefin copolymer and the electrolyte swellable thermoplastic polymer, wherein the compatibilizing agent is a liquid hydrocarbon, the compatibilizing agent having a boiling point in the range of 135-300° C., 
 (b) then, cooling the sheet material, whereby micropores are formed in the sheet material, and 
 (c) then, subjecting the sheet material to a stretching/vaporizing step, whereby at least a portion of the compatibilizing agent is removed from the sheet material, wherein the at least one cyclic olefin copolymer forms a continuous phase of the microporous sheet product and the electrolyte swellable thermoplastic polymer forms a discontinuous phase of the microporous sheet product, and wherein the microporous sheet product is free of polyethylene and polypropylene.